This invention relates to a bending device for use, for example, in an endoscope.
As is well known, an endoscope comprises a hollow body, a flexible insertion portion extending from a front end of the body, a flexible bending portion extending from a distal end of the insertion portion, and a rigid portion provided at a distal end of the bending portion. An inspection window and an illumination window are formed at the rigid portion.
Japanese Utility Model Publication No. 9274/77 discloses a flexible tube structure for an endoscope which structure includes one coil serving as a frame, and a resilient thin plate serving as a limitation member for limiting deformation of the coil. FIG. 1 of Japanese Laid-Open (Kokai) Utility Model Application No. 10605/80 shows an example in which this flexible tube structure is applied to a bending portion of an endoscope. More specifically, in the bending portion, the resilient thin plate is received in an internal space defined by the coil and extends in the longitudinal direction of the coil. Recesses are formed in each of opposite lateral edges of the resilient thin plate, and are juxtaposed in the longitudinal direction of this plate. The turn portions of the coil are engaged in the recesses. The bending portion is bent in a direction perpendicular to the plane of the resilient thin plate by an operating wire, so as to direct an inspection window and an illumination window of the rigid portion toward a desired direction.
The above resilient thin plate performs two functions. The first function is to prevent the coil from being axially compressed (that is, to prevent the turn portions of the coils from moving toward one another) when pulling the operating wire, thereby ensuring a proper bending of the bending portion. The second function is to limit the direction of bending of the bending portion to a direction perpendicular to the plane of the resilient thin plate.
The above bending portion is simple in construction, and can be easily manufactured. However, when due to an external force applied to the coil, the coil is bulged or expanded radially outwardly in a direction passing through the diametrically-opposite portions of the coil engaged respectively with the opposite lateral edges of the resilient thin plate, the resilient thin plate sometimes is disengaged from the coil. In this case, when the coil is returned to its initial configuration upon removal of the external force, the resilient thin plate becomes engaged with the coil in such a manner that the former is displaced out of position with respect to the latter. When such displacement of the resilient thin plate with respect to the coil occurs, a smooth bending operation can not be effected, and a desired bending angle can not be obtained.
The above Japanese Laid-Open Utility Model Application No. 10605/80 shows, in FIGS. 3 to 8, examples in which a number of pieces of a circular cross-section are used as the limitation members. These pieces are received within the internal space of the coil, and are juxtaposed in the axial direction of the coil. Each of the pieces has recesses at each of its opposite sides, and the turn portions of the coil are engaged in the recesses of the piece. Referring to the example shown in FIG. 5 of this prior publication, each adjacent pieces are held in contact with each other only at their two portions, so that the pieces allow the coil to be bent only in a direction perpendicular to a plane including those portions of the pieces contacting with each other. This conventional construction also has a drawback that the turn portions of the coil may be disengaged from the recesses of the pieces.